The present invention relates generally to gauging devices and more particularly to a dial indicator gauge which may be utilized in accurately measuring the internal diameters of thin-walled containers.
While not limited to any particular field of use, the invention is particularly adapted for measuring the internal diameter of a drawn and ironed container.
Recent advances in the manufacture of drawn and ironed containers has resulted in having the technology developed to a point where a 12 ounce drawn and ironed container may be manufactured from a circular disc having a thickness on the order of 0.0135 inches. In manufacturing such a container, the ultimate thickness of the sidewall of the drawn and ironed container is on the order of 0.003 inches and is, therefore, very flexible. Thus, in many instances, the internal wall of the container is not truly circular after the drawing and ironing process has been completed. In view of the noncircularity of the internal diameter of the container, difficulties have been encountered in accurately measuring the diameter of the container to determine whether it meets with certain specifications.
One type of gauge that has been proposed for measuring containers of this type is disclosed in U.S. Pat. No. 3,289,308. This patent discloses a mechanism wherein the spring pressure of a spring unit interposed between a pair of plug elements is adjustable for varying the force exerted on the internal surface of a circular wall that is being measured. One of the difficulties with this type of gauge for accurately measuring the internal diameter of a drawn and ironed container is the fact that only the upper edge of the internal diameter can be measured. It will be appreciated that in the formation of a drawn and ironed container, the portion of the container sidewall which is adjacent the upper free edge is normally purposely made slightly thicker than the remainder of the container wall since this portion is utilized as a flange for seaming an end to the container after the contents have been inserted therein. Thus, the measurement of the upper edge of the drawn and ironed container is not a true reflection of the actual diameter of the remainder of the container. Furthermore, the complicated nature of the structure disclosed in this patent substantially increases the cost and it is believed that the accuracy of such a unit is limited.